Structure and Entanglement Factors on Dynamics of Polymer-Grafted Nanoparticles

Abstract

Nanoparticles functionalized with long polymer chains at low graft density are interesting systems to study structure−dynamic relationships in polymer nanocomposites since they are shown to aggregate into strings in both solution and melts and also into spheres and branched aggregates in the presence of free polymer chains. This work investigates structure and entanglement effects in composites of polystyrene-grafted iron oxide nanoparticles by measuring particle relaxations using X-ray photon correlation spectroscopy. Particles within highly ordered strings and aggregated systems experience a dynamically heterogeneous environment displaying hyperdiffusive relaxation commonly observed in jammed soft glassy systems. Furthermore, particle dynamics is diffusive for branched aggregated structures which could be caused by less penetration of long matrix chains into brushes. These results suggest that particle motion is dictated by the strong interactions of chains grafted at low density with the host matrix polymer.

Polymer-functionalized polymer nanoparticles and their behaviour in suspensions

“…3,23,24 The behaviour of such nanoparticles dispersed in a polymer matrix has been shown to depend on the composition of the canopy as determined by the degree of polymerization (N) and grafting density (σ) of the chains since these parameters influence both the particle/particle interaction and the particle/environment interaction. 25,26 The influence of N and σ on the stability of polymer functionalized nanoparticles dispersed in a solvent or in a solid matrix has been widely studied for nanoparticles with a rigid core. In such systems, the dynamics of the nanoparticle suspensions and the particle/particle interactions in suspension were mostly governed by the architecture of the polymer canopy 27 via the excluded volume interactions and chain configuration entropy, 28,29 and fluctuations of the polymer canopy influenced the fragility of the particle assemblies.…”

Grafted polymer chains suppress nanoparticle diffusion in athermal polymer melts

“…This sub-diffusive behavior was attributed to the penetration of short matrix chains into the brush. Kandar et al 30 31 These studies all suggest that the diffusion of polymer-grafted NPs is closely connected to the nature of the grafted layer, namely, the dynamics of the grafted polymer chains and the interpenetration between the brush and matrix chains. We measure the diffusion coefficient of NPs grafted with poly(methyl methacrylate) (PMMA) chains of molecular weight N = 16 or 21 kg/mol and varying grafting density (σ) in unentangled to slightly entangled PMMA melts of varying matrix molecular weight P = 4-52 kg/mol.…”

Ordering Polymer‐Grafted Nanoparticles at Oil–Air Interfaces under Magnetic Fields

“…In this study, particles with long grafted chains are examined to demonstrate long‐range ordering in monolayers. Particles that were shown to organize into strings and dispersed structures in solution and also in their composite forms are, herein, examined in their thin films at oil–air interfaces. It is important to note that the grafted layer of our particles is not dense or crosslinked to form uniform density of chains as in the particles assembled into ordered structures in monolayers .…”